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A study of small-scale CO2 accidental release in near-field from a pressurized pipeline
Available online at www.sciencedirect.com
ScienceDirect Availableonline onlineatatwww.sciencedirect.com www.sciencedirect.com Available Energy Procedia 00 (2017) 000–000
ScienceDirect ScienceDirect
www.elsevier.com/locate/procedia
Energy Procedia 142 Energy Procedia 00(2017) (2017)3234–3239 000–000 www.elsevier.com/locate/procedia
9th International Conference on Applied Energy, ICAE2017, 21-24 August 2017, Cardiff, UK
A study of small-scale CO2 accidental release in near-field from a The 15th International Symposium on District Heating and Cooling pressurized pipeline Assessing the Zhou feasibility heat demand-outdoor b b using the Kang Lia,*, Xuejin , Ran Tuof , Qiyuan Xiec, Jianxin Yic and Xi Jiangd,** temperature function for a long-term district heat demand forecast School of Energy and Power Engineering, University of Shanghai for Science and Technology, Shanghai 200093, China a
b
College of Mechanical Engineering and Automation, Huaqiao University, Xiamen, Fujian 361021, China
a a c of Safety Engineering & State Key bLaboratory of Fire Science, I. Andrića,b,cDepartment *, A. Pina , P.Science Ferrão , J. Fournier ., B. Lacarrière , O. Le Correc c
a
University of Science and Technology of China, Hefei, Anhui 230026, China d School Engineering and Materials Science, Queen -Mary University of Técnico, London, Mile End Road, E1 4NS, UK Portugal IN+ Center for of Innovation, Technology and Policy Research Instituto Superior Av. Rovisco PaisLondon 1, 1049-001 Lisbon, b Veolia Recherche & Innovation, 291 Avenue Dreyfous Daniel, 78520 Limay, France c Département Systèmes Énergétiques et Environnement - IMT Atlantique, 4 rue Alfred Kastler, 44300 Nantes, France
Abstract
The near-field of the supercritical CO2 leakage from a damaged pipeline involves complex phase transition and kinetic effects Abstract with significant influences on the development of the leakage process. Experiments were conducted to obtain the early stage flow characteristics of the jet plume in the near-field. The velocity in the centerline of jet plume was also measured from different Districtsizes heating networks are commonly the literature asprocess one ofduring the most decreasingwas the leakage showing a close relationshipaddressed with the in depressurization the effective leakage. solutions Numericalforsimulation greenhouse emissions fromwave the building These systems high investments returned the through the heat conducted to gas capture the shock structuresector. including Mach disk, require barrel shock and reflectedwhich shock,arevalidating observation to thekinetic changed climate andThe building renovation heat demand in the future could decrease, ofsales. theseDue near-field effects in theconditions experiments. velocity variationspolicies, in the near-field were also calculated and compared prolonging the investment returnwith period. with experimental measurements an acceptable accuracy. The main scope of this paper is to assess the feasibility of using the heat demand – outdoor temperature function for heat demand districtPublished of Alvalade, locatedLtd. in Lisbon (Portugal), was used as a case study. The district is consisted of 665 ©forecast. 2017 TheThe Authors. by Elsevier buildings that vary in both construction period and typology. weather scenarios (low,onmedium, and three district Peer-review under responsibility of the scientific committee of theThree 9th International Conference Appliedhigh) Energy. renovation scenarios were developed (shallow, intermediate, deep). To estimate the error, obtained heat demand values were comparedcarbon with capture results and fromstorage; a dynamic heat demand model,transport; previously developed andwave validated by the authors. Keywords: supercritical CO2; pipeline choked flow; shock structure The results showed that when only weather change is considered, the margin of error could be acceptable for some applications (the error in annual demand was lower than 20% for all weather scenarios considered). However, after introducing renovation scenarios, the error value increased up to 59.5% (depending on the weather and renovation scenarios combination considered). The value of slope coefficient increased on average within the range of 3.8% up to 8% per decade, that corresponds to the decrease in the number of heating hours of 22-139h during the heating season (depending on the combination of weather and renovation scenarios considered). On the other hand, function intercept increased for 7.8-12.7% per decade (depending on the coupled scenarios). The values suggested could be used to modify the function parameters for the scenarios considered, and improve the accuracy of heat demand estimations. * 2017 Corresponding author.Published Tel.: +86-1801-9754927; © The Authors. by Elsevier Ltd. E-mail address: [email protected]. Peer-review under responsibility of the Scientific Committee of The 15th International Symposium on District Heating and ** Corresponding author. Tel.: +44-20-7882-5002; Cooling. E-mail address: [email protected].
Keywords: Heat demand; Forecast; Climate change 1876-6102 © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the scientific committee of the 9th International Conference on Applied Energy.
1876-6102 © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the Scientific Committee of The 15th International Symposium on District Heating and Cooling.
1876-6102 © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the scientific committee of the 9th International Conference on Applied Energy. 10.1016/j.egypro.2017.12.496
2
Kang Li et al. / Energy Procedia 142 (2017) 3234–3239 Author name / Energy Procedia 00 (2017) 000–000
3235
1. Introduction Power generation using fossil fuels contributes significantly to the increase of carbon dioxide concentration in the atmosphere and the consequent global warming. In the foreseeable future the traditional fossil fuels will still supply most of energy source in spite of the quick development of the cleaner and renewable energy supply [1]. To meet challenges between the current energy consumption structure and the tendency of global warming, carbon capture and storage (CCS) provides a possibility of large reduction of CO2 emissions from fossil-fueled power plants and industrial processes, providing an opportunity for power plants from decommission in a carbon-constrained world. Carbon capture, transportation and storage are the three main parts in CCS while effectiveness, cost and safety are the key issues, especially in the transportation of the CO2. Pipeline transportation is one of the most important ways in CO2 transportation which is not a new technology [2]. Over 6500 km of CO2 pipelines have been in operation for years mostly locating in North America, which are mainly used for CO2-enhanced oil recovery (CO2-EOR) projects and CO2 storage operations [3]. Generally, CO2 is pressurized into supercritical phase at 8 ~ 15 MPa for transportation which is most efficient and economical way [4]. Accidental release of CO2 from such a highly pressurized pipeline could lead to serious negative impact on the local environment and human beings nearby, therefore fundamental study and risk assessment on the leakage behaviour of highly pressurized CO2 are necessary for the safety concern of the pipeline transportation. In this paper, a supercritical CO2 leakage model capable of predicting the near-field fluid dynamics of multiphase jet flow and phase transition phenomena associated with the accidental CO2 release is presented. The results of a series of experimental measurements in small-scale CO2 accidental release are also presented, representing pipeline leakages under different conditions. The variation of the velocity in the near-field shown in this work illustrates the fluid dynamic behaviour of the under-expanded jet flow. The acquirement of correct thermodynamic phase during leakage process in the near-field is of particular importance in the numerical simulation given the very different hazard profiles of CO2. The modelling of CO2 fluid dynamics poses a number of quite unique challenges, and the theoretical developments presented in this model go some way to elucidating observed physics and providing suggestions for the further developments. Model validations have been undertaken by comparing with the experimental data obtained. 2. Experiments To investigate the behaviour of CO2 in the near-field, the characteristics of the choked flow at the leakage nozzle in the early stages of the leakage need to be measured firstly. The variation of velocity and temperature also need to be recorded as the fundamental data to analyze behaviour of CO2 in near-field. Details of the experiment setup are shown in Fig. 1.
Fig. 1. Details of the experiment setup.
Kang Li et al. / Energy Procedia 142 (2017) 3234–3239 Author name / Energy Procedia 00 (2017) 000–000
3236
3
A reduced-scale facility [5] was used to produce and store supercritical CO2 in the experiments. Dry supercritical CO2 are kept cycling in the main pipeline and a 10 meters long straight tube is chosen as the test section to operate the CO2 leakage experiment. Three anemometers are settled above the leakage nozzle to measure the velocity of jet flow with measurement accuracy of ±0.2%. The location of the anemometers is shown in Fig. 1(a). Twelve armored thermocouples and five pressure sensors are mounted along the pipeline to measure the variation of temperature and pressure during the leakage process. T1-T7 record the temperature of CO2 inside the pipeline and T8-T12 record the temperature of tube wall. Pressure sensor P6 is mounted at the leakage nozzle to obtain the outlet pressure of CO 2. The schematic of the test section in the facility is shown in Fig. 1(b). A pneumatic valve is mounted in the middle of the test section as the leakage nozzle. The structure of the pneumatic valve is shown in the Fig. 1(c). Four different sizes of the leakage nozzle are used in this experiment ranging from 0.5 mm to 5 mm. The details of the leakage nozzle are shown in Fig. 1(d). The operation conditions are summarized in Table 1. Table 1. Operating condition in the experiment Nozzle (diamet er)
Initial pressure (MPa)
HD DV
Anemomete rs after leak
Temperature (℃)
0.5
8.02
√
×
Ambient air
1
8.03
√
√
20±3
3
8.01
√
√
5
8.04
√
√
Initial CO2 in pipeline 40±1
3. Numerical modelling approach To investigate the structure of the multiphase jet flow in the near-field, numerical simulation approach has been conducted in validation of the experiment results. As the supercritical CO2 jet flow in the leakage process is a near axisymmetric free-jet supersonic expansion, time-dependent methods could be used to capture the shock wave structure including kinetic effects correctly. Along with the depressurization process, this method could also be extended to the viscous subsonic flow. The advantages and disadvantages of time-dependent methods simulating supercritical fluid flow have been fully discussed [6]. A finite difference, two-step Lax-Wendroff method was chosen as it is suitable for the hyperbolic partial differential equations of the free jet flow.
Fig. 2. Rectangular computational grid
4
Kang Li et al. / Energy Procedia 142 (2017) 3234–3239 Author name / Energy Procedia 00 (2017) 000–000
3237
In the calculation, a rectangular computational grid is used as shown in Fig. 2. The left boundary on all grid points above the orifice are settled with zero velocity in both axial and radian direction, while the temperature, pressure and density with the ambient conditions measured. The orifice boundary condition is based on the CO 2 leakage experiment results. For the top boundary and right boundary, the data are calculated by linear extrapolation using the two adjacent interior grid points. The symmetry boundary is used along the centerline. 4. Results and discussion 4.1. Shock wave structure in the near-field With known initial conditions of the pressure and mass outflow rate, the shock wave structure of the jet flow in the near-field could be simulated by the numerical method developed. In the experiment, supercritical CO2 from 8 MPa initial pressure at 1 mm leakage size was chosen to compare with the numerical simulation results. The details of shock wave structure of jet flow in the near-field are shown in Fig. 3.
Fig. 3. Shock wave structure of the jet flow in the near-field
The leaked highly pressurized CO2 depressurized rapidly and experienced an explosive expansion outside the leakage nozzle. When the pressure of CO2 at leakage nozzle decreased to about 6 MPa, a typical under-expanded plume structure could be clearly found which shown in Fig. 3(a). Due to the Joule-Thomson effect, the jet plume temperature around the leakage nozzle could drop rapidly below freezing point of the CO2 and a slim dry ice bank appeared at the bottom of the jet plume. In the numerical simulation of the CO 2 jet plume, the shock wave structure including barrel shock, reflected shock and Mach disk could also be observed in the near-field which is shown in Fig. 3(b). When the jet plume flow through the Mach disk, the compression effect would lead to a significant discontinuity of parameters like pressure, temperature and density of CO2. The difference of the CO2 density between Mach disk was clearly reflected in the variation of the refractive index and recorded by the High definition digital video (HD DV) which was validated by the numerical simulation.
3238
Kang Li et al. / Energy Procedia 142 (2017) 3234–3239 Author name / Energy Procedia 00 (2017) 000–000
5
4.2. Variation of velocity in the near-field To investigate the development of the multiphase jet plume in the near-field, three anemometers are settled 45 cm, 75 cm and 105 cm above the leakage nozzle. The velocities recorded at different leakage sizes are shown in Fig. 4.
Fig. 4. Velocity of jet plume above the leakage nozzle
The velocities of the jet plume were decreasing in the leakage process at different leakage sizes, and had a similar trend of decreasing rapidly in the transition stage with the development of the mass outflow caused by the pressure difference at the leakage nozzle. The jet plume became weakened with increased distance away from the leakage nozzle and the leakage nozzle size had different influences on the development of the velocity and the maximum speed the jet plume could reach. In comparison with the experimental data, the variation of velocity at 45 cm above the leakage nozzle from 1 mm size is chosen to be calculated through the numerical method introduced. The initial pressure at orifice was 8 MPa and the numerical results are shown in Fig. 5.
6
Author name / Energy Procedia 00 (2017) 000–000 Kang Li et al. / Energy Procedia 142 (2017) 3234–3239
3239
Fig. 5. The variation of the velocity calculated at 45 cm above the leakage nozzle
The results show that the velocity at 45 cm above the leakage nozzle calculated has a similar trend with as experimental data. The velocity dropped rapidly due to the large pressure difference at the leakage nozzle in the beginning and then reached a steady decreasing process later. The calculation results are fitted by a formula in Fig. 5 while the slope of the fitting line is smaller than the experimental data. Due the difference between the right boundary used in the calculation and the real conditions in the experiment, the numerical method had an underestimate of velocity with an error of about 10% in the beginning and a little overestimate after about 300 seconds. 5. Concluding remarks Experimental and numerical approaches have been used to investigate the leakage behaviour of supercritical CO2 in the near-field. The shock wave structure of the jet plume in the near-field were captured by the numerical approach. The results show an accurate simulation compared with the experiment. The velocity in the centerline of the jet plume were obtained showing that developments of the velocity field are influenced by the pressure difference at the leakage nozzle and varies with the leakage nozzle sizes. Numerical approach has been used to calculate the velocity of the jet plume in the near-field and compared with the experimental data. The numerical results show a similar trend of variation of the velocity but smaller slope than the experimental data due to difference of the boundary conditions. In the measurements, the accuracy and the repeatability of the data were verified by a series of repeatable experimental tests. References [1] M. Finley, B.P. statistical review of world energy. B.P. technical report, 2016. [2] F. Birol, World Energy Outlook 2014. IEA (International Energy Agency), 2015. [3] P. Noothout, F. Wiersma, O. Hurtado, D. Macdonald, J. Kemper, K. van Alphen, CO 2 pipeline infrastructure—lessons learnt. Energy Proc. 2014; 63: 2481–2492. [4] S. Joana, M. Joris, T. Evangelos, Technical and economical characteristics of CO 2 transmission pipeline infrastructure. Technical report, JRC Scientic andTechnical Reports, European Commission, 2011. [5] K. Li, X. Zhou, R. Tu, Q. Xie, X. Jiang, The flow and heat transfer characteristics of supercritical CO 2 leakage from a pipeline. Energy 2014; 71: 665-672. [6] I. Khalil, D. R. Miller, The Structure of Supercritical Fluid Free-Jet Expansions. AIChE Journal 2004; 50 (11): 2697-2704
ScienceDirect Availableonline onlineatatwww.sciencedirect.com www.sciencedirect.com Available Energy Procedia 00 (2017) 000–000
ScienceDirect ScienceDirect
www.elsevier.com/locate/procedia
Energy Procedia 142 Energy Procedia 00(2017) (2017)3234–3239 000–000 www.elsevier.com/locate/procedia
9th International Conference on Applied Energy, ICAE2017, 21-24 August 2017, Cardiff, UK
A study of small-scale CO2 accidental release in near-field from a The 15th International Symposium on District Heating and Cooling pressurized pipeline Assessing the Zhou feasibility heat demand-outdoor b b using the Kang Lia,*, Xuejin , Ran Tuof , Qiyuan Xiec, Jianxin Yic and Xi Jiangd,** temperature function for a long-term district heat demand forecast School of Energy and Power Engineering, University of Shanghai for Science and Technology, Shanghai 200093, China a
b
College of Mechanical Engineering and Automation, Huaqiao University, Xiamen, Fujian 361021, China
a a c of Safety Engineering & State Key bLaboratory of Fire Science, I. Andrića,b,cDepartment *, A. Pina , P.Science Ferrão , J. Fournier ., B. Lacarrière , O. Le Correc c
a
University of Science and Technology of China, Hefei, Anhui 230026, China d School Engineering and Materials Science, Queen -Mary University of Técnico, London, Mile End Road, E1 4NS, UK Portugal IN+ Center for of Innovation, Technology and Policy Research Instituto Superior Av. Rovisco PaisLondon 1, 1049-001 Lisbon, b Veolia Recherche & Innovation, 291 Avenue Dreyfous Daniel, 78520 Limay, France c Département Systèmes Énergétiques et Environnement - IMT Atlantique, 4 rue Alfred Kastler, 44300 Nantes, France
Abstract
The near-field of the supercritical CO2 leakage from a damaged pipeline involves complex phase transition and kinetic effects Abstract with significant influences on the development of the leakage process. Experiments were conducted to obtain the early stage flow characteristics of the jet plume in the near-field. The velocity in the centerline of jet plume was also measured from different Districtsizes heating networks are commonly the literature asprocess one ofduring the most decreasingwas the leakage showing a close relationshipaddressed with the in depressurization the effective leakage. solutions Numericalforsimulation greenhouse emissions fromwave the building These systems high investments returned the through the heat conducted to gas capture the shock structuresector. including Mach disk, require barrel shock and reflectedwhich shock,arevalidating observation to thekinetic changed climate andThe building renovation heat demand in the future could decrease, ofsales. theseDue near-field effects in theconditions experiments. velocity variationspolicies, in the near-field were also calculated and compared prolonging the investment returnwith period. with experimental measurements an acceptable accuracy. The main scope of this paper is to assess the feasibility of using the heat demand – outdoor temperature function for heat demand districtPublished of Alvalade, locatedLtd. in Lisbon (Portugal), was used as a case study. The district is consisted of 665 ©forecast. 2017 TheThe Authors. by Elsevier buildings that vary in both construction period and typology. weather scenarios (low,onmedium, and three district Peer-review under responsibility of the scientific committee of theThree 9th International Conference Appliedhigh) Energy. renovation scenarios were developed (shallow, intermediate, deep). To estimate the error, obtained heat demand values were comparedcarbon with capture results and fromstorage; a dynamic heat demand model,transport; previously developed andwave validated by the authors. Keywords: supercritical CO2; pipeline choked flow; shock structure The results showed that when only weather change is considered, the margin of error could be acceptable for some applications (the error in annual demand was lower than 20% for all weather scenarios considered). However, after introducing renovation scenarios, the error value increased up to 59.5% (depending on the weather and renovation scenarios combination considered). The value of slope coefficient increased on average within the range of 3.8% up to 8% per decade, that corresponds to the decrease in the number of heating hours of 22-139h during the heating season (depending on the combination of weather and renovation scenarios considered). On the other hand, function intercept increased for 7.8-12.7% per decade (depending on the coupled scenarios). The values suggested could be used to modify the function parameters for the scenarios considered, and improve the accuracy of heat demand estimations. * 2017 Corresponding author.Published Tel.: +86-1801-9754927; © The Authors. by Elsevier Ltd. E-mail address: [email protected]. Peer-review under responsibility of the Scientific Committee of The 15th International Symposium on District Heating and ** Corresponding author. Tel.: +44-20-7882-5002; Cooling. E-mail address: [email protected].
Keywords: Heat demand; Forecast; Climate change 1876-6102 © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the scientific committee of the 9th International Conference on Applied Energy.
1876-6102 © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the Scientific Committee of The 15th International Symposium on District Heating and Cooling.
1876-6102 © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the scientific committee of the 9th International Conference on Applied Energy. 10.1016/j.egypro.2017.12.496
2
Kang Li et al. / Energy Procedia 142 (2017) 3234–3239 Author name / Energy Procedia 00 (2017) 000–000
3235
1. Introduction Power generation using fossil fuels contributes significantly to the increase of carbon dioxide concentration in the atmosphere and the consequent global warming. In the foreseeable future the traditional fossil fuels will still supply most of energy source in spite of the quick development of the cleaner and renewable energy supply [1]. To meet challenges between the current energy consumption structure and the tendency of global warming, carbon capture and storage (CCS) provides a possibility of large reduction of CO2 emissions from fossil-fueled power plants and industrial processes, providing an opportunity for power plants from decommission in a carbon-constrained world. Carbon capture, transportation and storage are the three main parts in CCS while effectiveness, cost and safety are the key issues, especially in the transportation of the CO2. Pipeline transportation is one of the most important ways in CO2 transportation which is not a new technology [2]. Over 6500 km of CO2 pipelines have been in operation for years mostly locating in North America, which are mainly used for CO2-enhanced oil recovery (CO2-EOR) projects and CO2 storage operations [3]. Generally, CO2 is pressurized into supercritical phase at 8 ~ 15 MPa for transportation which is most efficient and economical way [4]. Accidental release of CO2 from such a highly pressurized pipeline could lead to serious negative impact on the local environment and human beings nearby, therefore fundamental study and risk assessment on the leakage behaviour of highly pressurized CO2 are necessary for the safety concern of the pipeline transportation. In this paper, a supercritical CO2 leakage model capable of predicting the near-field fluid dynamics of multiphase jet flow and phase transition phenomena associated with the accidental CO2 release is presented. The results of a series of experimental measurements in small-scale CO2 accidental release are also presented, representing pipeline leakages under different conditions. The variation of the velocity in the near-field shown in this work illustrates the fluid dynamic behaviour of the under-expanded jet flow. The acquirement of correct thermodynamic phase during leakage process in the near-field is of particular importance in the numerical simulation given the very different hazard profiles of CO2. The modelling of CO2 fluid dynamics poses a number of quite unique challenges, and the theoretical developments presented in this model go some way to elucidating observed physics and providing suggestions for the further developments. Model validations have been undertaken by comparing with the experimental data obtained. 2. Experiments To investigate the behaviour of CO2 in the near-field, the characteristics of the choked flow at the leakage nozzle in the early stages of the leakage need to be measured firstly. The variation of velocity and temperature also need to be recorded as the fundamental data to analyze behaviour of CO2 in near-field. Details of the experiment setup are shown in Fig. 1.
Fig. 1. Details of the experiment setup.
Kang Li et al. / Energy Procedia 142 (2017) 3234–3239 Author name / Energy Procedia 00 (2017) 000–000
3236
3
A reduced-scale facility [5] was used to produce and store supercritical CO2 in the experiments. Dry supercritical CO2 are kept cycling in the main pipeline and a 10 meters long straight tube is chosen as the test section to operate the CO2 leakage experiment. Three anemometers are settled above the leakage nozzle to measure the velocity of jet flow with measurement accuracy of ±0.2%. The location of the anemometers is shown in Fig. 1(a). Twelve armored thermocouples and five pressure sensors are mounted along the pipeline to measure the variation of temperature and pressure during the leakage process. T1-T7 record the temperature of CO2 inside the pipeline and T8-T12 record the temperature of tube wall. Pressure sensor P6 is mounted at the leakage nozzle to obtain the outlet pressure of CO 2. The schematic of the test section in the facility is shown in Fig. 1(b). A pneumatic valve is mounted in the middle of the test section as the leakage nozzle. The structure of the pneumatic valve is shown in the Fig. 1(c). Four different sizes of the leakage nozzle are used in this experiment ranging from 0.5 mm to 5 mm. The details of the leakage nozzle are shown in Fig. 1(d). The operation conditions are summarized in Table 1. Table 1. Operating condition in the experiment Nozzle (diamet er)
Initial pressure (MPa)
HD DV
Anemomete rs after leak
Temperature (℃)
0.5
8.02
√
×
Ambient air
1
8.03
√
√
20±3
3
8.01
√
√
5
8.04
√
√
Initial CO2 in pipeline 40±1
3. Numerical modelling approach To investigate the structure of the multiphase jet flow in the near-field, numerical simulation approach has been conducted in validation of the experiment results. As the supercritical CO2 jet flow in the leakage process is a near axisymmetric free-jet supersonic expansion, time-dependent methods could be used to capture the shock wave structure including kinetic effects correctly. Along with the depressurization process, this method could also be extended to the viscous subsonic flow. The advantages and disadvantages of time-dependent methods simulating supercritical fluid flow have been fully discussed [6]. A finite difference, two-step Lax-Wendroff method was chosen as it is suitable for the hyperbolic partial differential equations of the free jet flow.
Fig. 2. Rectangular computational grid
4
Kang Li et al. / Energy Procedia 142 (2017) 3234–3239 Author name / Energy Procedia 00 (2017) 000–000
3237
In the calculation, a rectangular computational grid is used as shown in Fig. 2. The left boundary on all grid points above the orifice are settled with zero velocity in both axial and radian direction, while the temperature, pressure and density with the ambient conditions measured. The orifice boundary condition is based on the CO 2 leakage experiment results. For the top boundary and right boundary, the data are calculated by linear extrapolation using the two adjacent interior grid points. The symmetry boundary is used along the centerline. 4. Results and discussion 4.1. Shock wave structure in the near-field With known initial conditions of the pressure and mass outflow rate, the shock wave structure of the jet flow in the near-field could be simulated by the numerical method developed. In the experiment, supercritical CO2 from 8 MPa initial pressure at 1 mm leakage size was chosen to compare with the numerical simulation results. The details of shock wave structure of jet flow in the near-field are shown in Fig. 3.
Fig. 3. Shock wave structure of the jet flow in the near-field
The leaked highly pressurized CO2 depressurized rapidly and experienced an explosive expansion outside the leakage nozzle. When the pressure of CO2 at leakage nozzle decreased to about 6 MPa, a typical under-expanded plume structure could be clearly found which shown in Fig. 3(a). Due to the Joule-Thomson effect, the jet plume temperature around the leakage nozzle could drop rapidly below freezing point of the CO2 and a slim dry ice bank appeared at the bottom of the jet plume. In the numerical simulation of the CO 2 jet plume, the shock wave structure including barrel shock, reflected shock and Mach disk could also be observed in the near-field which is shown in Fig. 3(b). When the jet plume flow through the Mach disk, the compression effect would lead to a significant discontinuity of parameters like pressure, temperature and density of CO2. The difference of the CO2 density between Mach disk was clearly reflected in the variation of the refractive index and recorded by the High definition digital video (HD DV) which was validated by the numerical simulation.
3238
Kang Li et al. / Energy Procedia 142 (2017) 3234–3239 Author name / Energy Procedia 00 (2017) 000–000
5
4.2. Variation of velocity in the near-field To investigate the development of the multiphase jet plume in the near-field, three anemometers are settled 45 cm, 75 cm and 105 cm above the leakage nozzle. The velocities recorded at different leakage sizes are shown in Fig. 4.
Fig. 4. Velocity of jet plume above the leakage nozzle
The velocities of the jet plume were decreasing in the leakage process at different leakage sizes, and had a similar trend of decreasing rapidly in the transition stage with the development of the mass outflow caused by the pressure difference at the leakage nozzle. The jet plume became weakened with increased distance away from the leakage nozzle and the leakage nozzle size had different influences on the development of the velocity and the maximum speed the jet plume could reach. In comparison with the experimental data, the variation of velocity at 45 cm above the leakage nozzle from 1 mm size is chosen to be calculated through the numerical method introduced. The initial pressure at orifice was 8 MPa and the numerical results are shown in Fig. 5.
6
Author name / Energy Procedia 00 (2017) 000–000 Kang Li et al. / Energy Procedia 142 (2017) 3234–3239
3239
Fig. 5. The variation of the velocity calculated at 45 cm above the leakage nozzle
The results show that the velocity at 45 cm above the leakage nozzle calculated has a similar trend with as experimental data. The velocity dropped rapidly due to the large pressure difference at the leakage nozzle in the beginning and then reached a steady decreasing process later. The calculation results are fitted by a formula in Fig. 5 while the slope of the fitting line is smaller than the experimental data. Due the difference between the right boundary used in the calculation and the real conditions in the experiment, the numerical method had an underestimate of velocity with an error of about 10% in the beginning and a little overestimate after about 300 seconds. 5. Concluding remarks Experimental and numerical approaches have been used to investigate the leakage behaviour of supercritical CO2 in the near-field. The shock wave structure of the jet plume in the near-field were captured by the numerical approach. The results show an accurate simulation compared with the experiment. The velocity in the centerline of the jet plume were obtained showing that developments of the velocity field are influenced by the pressure difference at the leakage nozzle and varies with the leakage nozzle sizes. Numerical approach has been used to calculate the velocity of the jet plume in the near-field and compared with the experimental data. The numerical results show a similar trend of variation of the velocity but smaller slope than the experimental data due to difference of the boundary conditions. In the measurements, the accuracy and the repeatability of the data were verified by a series of repeatable experimental tests. References [1] M. Finley, B.P. statistical review of world energy. B.P. technical report, 2016. [2] F. Birol, World Energy Outlook 2014. IEA (International Energy Agency), 2015. [3] P. Noothout, F. Wiersma, O. Hurtado, D. Macdonald, J. Kemper, K. van Alphen, CO 2 pipeline infrastructure—lessons learnt. Energy Proc. 2014; 63: 2481–2492. [4] S. Joana, M. Joris, T. Evangelos, Technical and economical characteristics of CO 2 transmission pipeline infrastructure. Technical report, JRC Scientic andTechnical Reports, European Commission, 2011. [5] K. Li, X. Zhou, R. Tu, Q. Xie, X. Jiang, The flow and heat transfer characteristics of supercritical CO 2 leakage from a pipeline. Energy 2014; 71: 665-672. [6] I. Khalil, D. R. Miller, The Structure of Supercritical Fluid Free-Jet Expansions. AIChE Journal 2004; 50 (11): 2697-2704